[FieldTrip] EEG rereferencing with REST method

[Min-Young Kim]

Yes, I read Dong et al’s paper published in Frontiers in Neuroscience (2017). In the paper, the REST EEG was expressed in two equations

(1)   V_REST = R_AR * V_AR

(2)   V_REST = V_AR + l*average(V_REST)

, where the V_REST in (2) was calculated by using (1). At first, I assumed that (1) was enough to get V_REST, but now I figured out that (2) was used to get better approximation of V_REST. I will check whether my leadfield was calculated properly. The 2nd term in (2), i.e., l*average(V_REST), was order of 10^(-20), which was why my V_AR and V_REST were almost the same. Maybe I messed up with some unit conversions. Wish me luck!

 

All the best,

Min-Young

 

Min-Young Kim, Ph.D.

Tel: +82) 42 - 868 - 5204 (Office)

Email:  <mailto:mykim at kriss.re.kr> mykim at kriss.re.kr

Quantum Technology Institute

Korea Research Institute of Standards and Science

 

 

 

From: fieldtrip [mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Schoffelen, J.M. (Jan Mathijs)
Sent: Wednesday, October 21, 2020 4:49 PM
To: FieldTrip discussion list <fieldtrip at science.ru.nl>
Subject: Re: [FieldTrip] EEG rereferencing with REST method

 

Hi Min-Young, 

 

Did you check the original paper that is referenced in the code? I suggest to start there.

 

Also, re-referencing to the average is achieved by subtraction of the mean over channels, i.e. : data - mean(data)

The line you refer to is adding the mean of some variable (data_z) to data, which is not average rereferencing.

 

Best wishes,

Jan-Mathijs

 





On 21 Oct 2020, at 04:06, Min-Young Kim <mykim at kriss.re.kr <mailto:mykim at kriss.re.kr> > wrote:

 

Dear FieldTrippers,

 

I am working with 19 Ch EEG data acquired with Biosemi system. To test re-reference options, I tried average earlobes, common average, and REST methods in the preprocessing. However, I found that the EEG for REST was almost the same as the EEG for common average. When I looked at the ft_preproc_rereference.m, the line 141 says 

>>data_z = G * pinv(Gar, 0.05) * data;

But then in line 144

>>data_z = data + repmat(mean(data_z), size(G,1), 1);

 

Isn’t the line 141 enough to generate REST EEG signals? To me, the line 144 seems to be the common average referenced EEG data. I would appreciate if someone explains the meaning of the line 144.

 

Thanks,

Min-Young

 

Min-Young Kim, Ph.D.

Tel: +82) 42 - 868 - 5204 (Office)

Email:  <mailto:mykim at kriss.re.kr> mykim at kriss.re.kr

Quantum Technology Institute

Korea Research Institute of Standards and Science

 

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